WO2002053347A1

WO2002053347A1 - Foam injection molding method

Info

Publication number: WO2002053347A1
Application number: PCT/JP2001/011473
Authority: WO
Inventors: Hiroshi Yamaki; Yuji Tanaka
Original assignee: Asahi Kasei Kabushiki Kaisha
Priority date: 2000-12-27
Filing date: 2001-12-26
Publication date: 2002-07-11
Also published as: CN1484576A; DE10197126T1; US20040108612A1; CN1273277C; US7077987B2; JPWO2002053347A1

Abstract

A foam injection molding method, comprising the steps of providing a metal mold having a molten resin discharge means in the inside wall surface of a metal mold cavity, forming a foaming molten resin lump in the metal mold cavity by injecting a foaming thermoplastic resin, and pressing the surface of the foaming molten resin lump against the inside wall surface of the metal mold cavity by applying a pressure to the foaming molten resin lump inside the metal mold cavity to solidify the surface part of the foaming molten resin lump so as to form the skin layer of the foaming molten resin lump, and discharging a part of the foaming molten resin lump to the outside of the metal mold cavity through the molten resin discharge means by the foaming pressure of the foaming molten resin lump itself to lower the pressure applied to the foaming molten resin lump so as to form a foaming resin lump having a substantially foamless skin layer by foaming the foaming molten resin lump in the metal mold cavity, whereby a light foam mold product with high dimensional accuracy can be formed economically with a high productivity by accurately transferring the shape of the inside wall surface of the metal mold cavity.

Description

Description Foam injection molding method Technical field

The present invention relates to a method for foam injection molding of a thermoplastic resin. More specifically, the present invention relates to a method for foaming and injection molding a thermoplastic resin for molding a foamed molded article having a substantially non-foamed skin layer, comprising: (1) a fixed half mold and a combination with the fixed mold half; A mold having a mold cavity defined by the inner wall surface of the fixed mold half and the inner wall surface of the movable mold half; and an inner wall surface of the mold cavity. Has means for discharging molten resin,

(2) The foamable thermoplastic resin is injected into the mold cavity in a molten state to form a foamable molten resin mass in the mold cavity.

(3) By applying pressure to the foamable molten resin mass in the mold cavity and pressing the surface of the foamable molten resin mass against the inner wall surface of the mold cavity, the foamability is improved. The surface portion of the molten resin mass is solidified to form a skin layer of the foamable molten resin mass, and

(4) A part of the foamable molten resin mass is discharged to the outside of the mold cavity through the molten resin discharging means by a foaming pressure of the foamable molten resin mass itself, and the foamable molten resin mass is discharged. Pressure, thereby foaming the foamable molten resin mass in the mold cavity to have the substantially foamless skin layer The present invention relates to a foam injection molding method for forming a foamed resin mass. ADVANTAGE OF THE INVENTION According to the foam injection molding method of the present invention, the mold cavity has a good transferability of the inner wall surface shape, and a molded article having a non-foamed skin layer and a highly foamed foam layer can be reproduced efficiently, economically Not only can it be manufactured in a specific manner, but also the thickness of the skin layer of the molded article and the expansion ratio of the molded article can be easily controlled. According to the foam injection molding method of the present invention, various excellent thermoplastic resin foam injection molded articles such as housings for light electric appliances and electronic appliances, various automobile parts, various daily necessities and the like can be provided at low cost. In addition, the foam injection molding method of the present invention includes not only ordinary thermoplastic resins but also resin compositions which contain flame retardants having low thermal stability and which are difficult to mold at high resin temperatures, and It can be advantageously applied to resins that are difficult to injection-mold by the conventional method because of their low performance. Conventional technology

Conventionally, a foam injection molding method for producing a foam molded article obtained by foaming a foamable thermoplastic resin containing a foaming agent is known. As the foaming agent, azodicarbonamide (ADCA), Ν, Ν'-dinitrosopentamethylenetetramine (DΡΡ) or the like is generally used. The amount of the foaming agent is generally in the range of 1 to 5 parts by weight based on 100 parts by weight of the resin. As a typical example of the conventional foam injection molding method, there is a short shot method. In the short shot method, a blowing agent is included. The molten resin is injected into the mold cavity with a volume smaller than the volume of the mold cavity. The part of the molten resin injected into the mold cavity that first contacts the inner wall of the mold cavity is immediately cooled and solidified to form a solidified layer, and the molten resin that enters the mold cavity later. Flows through the center of the mold cavity along the solidified layer, reaches the flow front (flow front), then goes to the inner wall of the mold cavity, contacts the inner wall of the mold cavity, and is cooled. To form a solidified layer. That is, it has a flow behavior called a so-called fountain flow. After completion of the injection of the molten resin, the molten resin is advanced to the end of the mold cavity by foaming of the molten resin, and is filled with the mold cavity to form a foam molded article. This short shot method has the drawback that the resin surface of the molded article becomes rough because foaming occurs even at the leading end of the flowing molten resin, but it is the simplest molding method. Widely used.

On the other hand, as a technique for obtaining a thick-walled foamed article having a good appearance and a small amount of squeezing, generally, a counter plate as disclosed in Japanese Patent Publication No. 62-166166 is used. There is a molding method called sha molding method. This involves injecting a molten resin containing a foaming agent into a mold cavity filled with compressed air in a short shot, and then releasing the compressed air in the cavity out of the mold to form a cavity. A molding method that cools the resin while keeping the pressure on the molten resin inside low, and suppresses foaming at the front when filling the resin. This is a technology to create a molded product that has no foaming pattern on the surface of the molded product and only foams inside. In the counter pressure molding method, after the foaming molten resin is almost completely filled in the mold cavity in a non-foamed state, the molten resin inside the molded product is cooled, and the volume shrinkage accompanying cooling is foamed. . For this reason, the basic idea is that the amount of the foaming agent contained in the resin for the purpose of giving the resin foaming properties should be the minimum that can compensate for volume shrinkage by foaming. Therefore, in this method, since the resin is not pressed against the inner wall surface of the mold cavity with high pressure, the transferability of the mold surface is low, the appearance quality is poor, and only the volume shrinkage is foamed. Therefore, there is a limit in reducing the weight of molded products. Also, if the amount of the foaming agent contained in the resin is too large, foaming occurs even after the molded product is removed from the mold, and the molded product expands and deforms. There is a problem that requires a long cooling time.

As an old idea, a foamed molten resin is injected and filled into a mold cavity, a gas is injected into the molten resin, a hollow body is formed once, and a surface layer of the hollow body is formed. After the part is solidified, there is a method of discharging the injected gas body out of the mold and foaming the expandable molten resin into the hollow part. (Japanese Patent Publication No. 53-253052 (US Patent No. 4, 1 229, and 6335))). However, when trying to release gas from the gas supply port used to form the hollow space, the pressure loss in the piping etc. is large, and it takes time to discharge the gas body having the hollow space. . As a result, gas from the hollow During the release of the body, the solidification of the molten resin on the inner surface of the hollow part progresses, and a foam layer of a sufficient size cannot be formed. Also, in addition to the large amount of gas absorbed in the foaming molten resin, if the gas is to be released while the inner surface of the hollow part is foaming, it will also foam around the gas opening, which is the gas supply port. U. As a result, the gas body forming the hollow body cannot be quickly opened outside the mold, and the pressure of the gas body remains in the hollow part. Eventually, when the mold is opened or the molded product is removed, the molded product will burst.

Recently, a method has been proposed in which a hollow body is formed and then foamed in the same manner as described above. That is, Japanese Patent Application Laid-Open No. 7-32405 (corresponding to U.S. Patent No. 5,900,198 and U.S. Patent No. 5,948,446) and Japanese Patent Application Publication No. This is a publication of No. 2000-0-9446. According to the former document, when a foamable molten resin is injected into a mold cavity pressurized with a high-pressure gas, a high-pressure gas is injected into the molten resin during or after the injection to form a hollow portion. The injected high-pressure gas is discharged out of the mold, and the foamable molten resin is foamed into the hollow part to form a hollow part in the thick part of the injection molded product. There is disclosed a method for obtaining a resin molded product in which foam cells are interspersed and the surface of which does not have sink marks (JP-A-7-32405). However, this method also requires time for gas discharge as in the above-mentioned Japanese Patent Publication No. 53-253032 (corresponding to U.S. Pat. No. 4,129,635). Was As a result, it is not possible to form a foam layer of a sufficient size, and furthermore, foaming near the gas discharge port deteriorates gas outflow, causing the molded article to burst due to the pressure of the residual gas. is there.

On the other hand, in the latter document (Japanese Patent Publication No. 2000-094464), a molten resin containing a foaming agent is injected and filled in a mold cavity, and then added to the molten resin. A pressurized gas is injected and a part of the molten resin is discharged to a resin discharge cavity (spirover one-cavity) to form a hollow portion. Then, the pressurized gas in the hollow portion is discharged to remove the pressure. A method is disclosed for obtaining a lightweight molded article having a good appearance, high strength and high rigidity, which is provided with a substantially non-foamed layer on the surface and a foamed portion inside the layer by lowering the surface area. However, even in this method, when the molten resin is discharged into the resin discharging cavity, the gas in the hollow portion remains at a high pressure, so that even when the gas is discharged, the same method as in the former document is used. There is a problem (that is, a foam layer of a sufficient size cannot be formed, and a molded article bursts due to the pressure of the residual gas).

As described above, in the conventional foam molding method, there is no foam injection molding method capable of reducing the weight and shortening the molding cycle by a high foaming ratio while maintaining excellent appearance and dimensional accuracy. Was.

Furthermore, considering the case of performing a molding method to obtain a large number of molded articles by one molding, the conventional foam molding method is as follows. There is a problem. When two or more molded articles are to be molded simultaneously using a mold for simultaneously molding a plurality of molded articles, the respective mold cavities must be adjusted in order to achieve the same expansion ratio. The balance between the resin filling amount and the resin pressure must be balanced. In particular, when four or more molded products are to be molded at the same time, the conventional molding method has a problem that, in most cases, the above balance cannot be obtained, and products having the same expansion ratio cannot be obtained. Further, when obtaining a plurality of foamed molded products having different volumes in the same mold, it is more difficult to achieve the above balance. Thus, multi-cavity molding in foam molding is not actually used in mass production.

An object of the present invention is to provide a method for foam injection molding of a thermoplastic resin foam molded article, in which the shape of an inner wall surface of a mold cavity is transferred with high precision, and a lightweight foam molded article with high dimensional accuracy and high productivity is economically produced with high productivity. It is intended to provide a method for forming the target in a desired manner. Summary of the Invention

Under such circumstances, the present inventors have intensively studied to solve the above-mentioned problems. As a result, surprisingly, the foam injection molding method for a thermoplastic resin is (1) a fixed half mold and a movable half mold combined with the fixed half mold, and an inner wall surface of the fixed half mold and the movable half mold. A mold having a mold cavity defined by the inner wall surface of the mold is provided, and the inner wall surface of the mold cavity has a molten resin discharging means. (2) The foamable thermoplastic resin is injected into the mold cavity in a molten state to form a foamed molten resin mass in the mold cavity, and (3) the mold cavity is formed. By applying pressure to the foamable molten resin mass in the cavity and pressing the surface of the foamable molten resin mass against the inner wall surface of the mold cavity, the surface portion of the foamable molten resin mass is reduced. Solidifying to form a skin layer of the foamable molten resin mass; and (4) forming a part of the foamable molten resin mass by the foaming pressure of the foamable molten resin mass itself. It is discharged through the discharging means to the outside of the mold cavity to reduce the pressure on the foamable molten resin mass, whereby the foamable molten resin mass in the mold cavity is foamed. Forming a foamed resin mass having the skin layer which is substantially non-foamed. By foam injection molding method for it found that you can achieve the above object. In other words, according to the foam injection molding method described above, the mold cavity has good transferability of the inner wall surface shape, and a molded article having a non-foamed skin layer and a highly foamed foam layer can be reproducibly, efficiently, and efficiently. It has been found that not only can it be manufactured economically, but also the thickness of the skin layer of the molded article and the expansion ratio of the molded article can be easily controlled. Based on this finding, the present invention has been completed.

Accordingly, one object of the present invention is to provide a molded article having a mold cavity having good inner wall shape transferability and having a non-foamed skin layer and a highly foamed foam layer with good reproducibility and efficiency. Not only can it be manufactured economically, but also the thickness of the skin layer of the molded article and the development of the molded article An object of the present invention is to provide an excellent foam injection molding method capable of easily controlling a foam ratio.

The above and other objects of the present invention: Features and advantages will become apparent from the following detailed description and the appended claims, taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE FIGURES

1 (a) to 1 (c) are schematic diagrams showing one embodiment of the first method of the present invention.

FIG. 1 (a) is a schematic cross-sectional view showing a state of the inside of a mold before injection filling of a foamable molten resin.

FIG. 1 (b) is a schematic cross-sectional view showing a state inside the mold when injection filling of the molten resin is completed.

Fig. 1 (c) shows the molten resin discharge means (opening / closing valve 4) opened, a part of the molten resin mass in the mold cavity discharged to the molten resin discharge cavity, and the molten metal when foamed. FIG. 3 is a cross-sectional view showing a state inside a mold.

2 (a) to 2 (c) are schematic views showing one embodiment of the second method of the present invention.

FIG. 2 (a) is a schematic cross-sectional view showing a state inside the mold during injection filling of the foamable molten resin.

Fig. 2 (b) shows the interior of the mold when the injection of the molten resin is completed and the pressurized gas is injected to form a gas-filled hollow in the molten resin mass. It is a schematic sectional drawing which shows the state of.

Fig. 2 (c) shows that the molten resin discharge means (open / close valve 4) is opened, and a part of the molten resin mass and the pressurized gas in the gas-filled hollow part are discharged into the molten resin discharge cavity and foamed. FIG. 4 is a schematic cross-sectional view showing a state inside the mold when the mold is opened.

3 (a) to 3 (d) are schematic diagrams showing the method of the present invention used in Example 6. FIG.

FIG. 3 (a) is a schematic cross-sectional view showing the state of the inside of the mold before the injection and filling of the foamable molten resin.

FIG. 3 (b) is a schematic cross-sectional view showing the state inside the mold when the injection and filling of the molten resin is completed.

FIG. 3 (c) is a schematic cross-sectional view showing a state inside the mold when a pressurized gas is injected into the molten resin mass to form a gas-filled hollow portion after the injection and filling of the molten resin are completed.

Fig. 3 (d) shows the molten resin discharge means (opening / closing valve 4) opened, and a part of the molten resin mass and the pressurized gas in the gas-filled hollow are discharged to the molten resin discharge cavity and foamed. FIG. 4 is a schematic cross-sectional view showing a state inside the mold when the mold is opened.

FIG. 4 shows a schematic front view of one example of a movable half mold of a four-cavity mold that can be used in the method of the present invention.

FIG. 5 is a schematic diagram of an injection molding apparatus used in Examples and Comparative Examples. Explanation of reference numerals

1 Mold

1 a fixed half

1 b movable half mold

2 Mold cavity

3 Capacities for discharging molten resin

4 Molten resin discharge means (open / close valve)

5 Access passage

6 sprue

7 Runner

8 Foaming molten resin

9 Foam resin block (foam layer)

1 0 Skin layer

1 1 Gas-filled hollow

1 2 Injection nozzle

1 3 Pressurized gas nozzle

1 4 Gas supply hole (vent)

15 a to 15 c 〇 one ring

16 One-way gas supply Three-way valve

1 7 Lines leading to the gas opening

1 8 Gas inlet

1 9 'gas supply control device

2 0 'Injection cylinder 2 1 Gas supply line into foamable molten resin

2 2 Counter gas supply line to mold

2 3 Injection molding machine

24 Carbon oxide gas source or nitrogen gas In Figs. 1 (a) to 5, similar members and parts are indicated by similar reference numbers. Detailed description of the invention

According to one aspect of the present invention, there is provided a foam injection molding method of a thermoplastic resin, comprising:

(1) A mold comprising a fixed mold and a movable mold combined with the mold, and having a mold cavity defined by an inner wall surface of the fixed mold and an inner wall surface of the movable mold,

The mold cavity has an inner wall surface and communicates with a resin inlet.

The inner wall surface of the mold cavity has a molten resin discharging means,

(2) The foamable thermoplastic resin is injected in a molten state into the mold cavity through the resin inlet under a predetermined injection temperature and pressure conditions, and the amount of the foamable molten resin is determined by the predetermined injection temperature and pressure conditions. In the range of 95 to 110% by weight of the foamable molten resin having the same volume as the mold cavity as measured below, preferably 9 8 to: L 0 5% range,

As a result, a foamable molten resin mass is formed in the mold cavity,

(3) By applying pressure to the foamable molten resin mass in the mold cavity and pressing the surface of the foamed raw resin mass against the inner wall surface of the mold cavity, The surface portion of the foamable molten resin mass is solidified to form a skin layer of the foamable molten resin mass, and

(4) A part of the foamable molten resin mass is discharged to the outside of the mold cavity through the molten resin discharging means by a foaming pressure of the foamable molten resin mass itself, and the foamable molten resin mass is discharged. The pressure on the mass is reduced, thereby foaming the foamable molten resin mass within the mold cavity to form a substantially non-foamed foamed resin mass having the skin layer. ,

A foam injection molding method characterized by this is provided. According to another aspect of the present invention, there is provided a method for foam injection molding of a thermoplastic resin, comprising:

(1) A mold comprising a fixed mold and a movable mold combined with the mold, and having a mold cavity defined by the inner wall surface of the fixed mold and the inner wall surface of the movable mold. ,

The mold cavity has an inner wall surface and communicates with the resin inlet and, if desired, the gas inlet. The inner wall surface of the mold cavity has a molten resin discharging means,

(2) The foamable thermoplastic resin is injected in a molten state into the mold cavity through the resin inlet under a predetermined injection temperature and pressure conditions, and the amount of the foamable molten resin is determined by the predetermined injection temperature and pressure conditions. In the range of 55 to 110%, preferably in the range of 60 to 100% of the weight of the foamable molten resin having the same volume as that of the mold cavity as measured below. And

As a result, a foamable molten resin mass is formed in the mold cavity,

(3) A pressurized gas is injected into the foamable molten resin mass in the mold cavity through the resin inlet or the gas inlet to form a gas-filled hollow portion in the foamable molten resin mass. Thus, by applying pressure to the foamable molten resin mass and pressing the outer surface of the foamable molten resin mass against the inner wall surface of the mold cavity, an outer surface portion of the foamable molten resin mass is obtained. To form a skin layer of the foamable molten resin mass,

Performing step (3) during step (2), after completion of step (2), or during and after step (2); and

(4) A part of the foamable molten resin mass and at least a part of the pressurized gas in the gas-filled hollow portion are subjected to the foaming pressure of the foamable molten resin mass itself and the pressure in the gas-filled hollow portion. Due to the pressure of the pressurized gas, the outside of the mold cavity is discharged through the molten resin discharging means. Discharging to reduce the pressure on the foamable molten resin mass, thereby foaming the foamable molten resin mass in the mold cavity to form a foam having the substantially non-foamed skin layer. Forming a resin mass,

A foam injection molding method characterized by this is provided. Next, in order to facilitate understanding of the present invention, basic features and preferred embodiments of the present invention will be listed.

1. A foam injection molding method for thermoplastic resin,

The mold cavity has an inner wall surface and communicates with a resin inlet.

The inner wall surface of the mold cavity has a molten resin discharging means,

(2) The foamable thermoplastic resin is injected in a molten state into the mold cavity through the resin inlet under a predetermined injection temperature and pressure conditions, and the amount of the foamable molten resin is determined by the predetermined injection temperature and pressure conditions. Measured in the range of 95 to 110% of the weight of the foamable molten resin having the same volume as the volume of the mold cavity,

As a result, a foamable molten resin mass is formed in the mold cavity. And

(2) A part of the foamable molten resin mass is discharged to the outside of the mold cavity through the molten resin discharging means by a foaming pressure of the foamable molten resin mass itself, and the foamable molten resin mass is discharged. Reducing the pressure on the foamed molten resin mass in the mold cavity to form a substantially non-foamed foamed resin mass having the skin layer.

A foam injection molding method characterized by the above.

2. Pressing the foamable molten resin mass in step (3), injecting additional foamable molten resin into the mold cavity and applying a predetermined resin holding pressure to the foamable molten resin mass 2. The method according to item 1, wherein the method is performed.

3. Before step (2) and after step (1), pressurized gas is introduced into the mold cavity to reduce the pressure of the mold cavity.

(1) wherein the pressure at which the foamable molten resin injected in (2) does not cause foaming at its flow front is set to Is the method described in 2.

4. The method according to the above item 3, wherein the pressurized gas introduced into the mold cap before the step (2) and after the step (1) is carbon dioxide gas.

5. The molten resin discharging means of the mold cavity is an on-off valve, and the mold has a molten resin discharging cavity communicating with the mold cavity via the on-off valve. The volume of the molten resin discharging cavity is larger than the volume of the part of the foamable molten resin mass discharged to the outside of the mold cavity through the on-off valve in step (4). The method according to any one of the above items 1 to 4, characterized in that:

6. The method according to the above item 5, wherein the molten resin discharging cavity has an air opening communicating with the outside of the mold.

7. The foamable molten resin is composed of the molten resin and at least one gaseous foaming agent dissolved therein, and the at least one gaseous foaming agent is carbon dioxide gas and carbon dioxide gas. 7. The method according to any one of items 1 to 6, wherein the method is selected from the group consisting of:

8. The content of the foaming agent in the foamable molten resin is 0.05 to 10%. 8. The method according to the above item 7, wherein the method is characterized in that the amount is by weight.

9. A foam injection molding method for a thermoplastic resin,

The mold cavity has an inner wall surface and communicates with a resin inlet and, if desired, a gas inlet.

■ The inner wall surface of the mold cavity has a molten resin discharging means,

(2) The foamable thermoplastic resin is injected in a molten state into the mold cavity through the resin inlet under a predetermined injection temperature and pressure conditions, and the amount of the foamable molten resin is determined by the predetermined injection temperature and pressure conditions. Measured in the range of 55 to 110% by weight of the foamable molten resin having the same volume as the mold cavity,

As a result, a foamable molten resin mass is formed in the mold cavity,

(3) A pressurized gas is injected into the foamable molten resin mass in the mold cavity through the resin inlet or the gas inlet to form a gas-filled hollow portion in the foamable molten resin mass. Thus, by applying pressure to the foamable molten resin mass and pressing the outer surface of the foamable molten resin mass against the inner wall surface of the mold cavity, the outer surface of the foamable molten resin mass is obtained. Solidifies the part, Forming the skin layer of the molten resin mass,

(4) At least a part of the foamable molten resin mass and at least a part of the pressurized gas in the gas-filled hollow portion are combined with the foaming pressure of the foamable molten resin mass itself and the pressure in the gas-filled hollow portion. The pressure of the pressurized gas is discharged through the molten resin discharging means to the outside of the mold cavity to reduce the pressure on the foamable molten resin mass, thereby reducing the pressure in the mold cavity. Foaming the foamable molten resin mass to form a substantially non-foamed foamed resin mass having the skin layer;

A foam injection molding method characterized by the above.

10. The method according to the above item 9, wherein the pressurized gas used in the step (3) is carbon dioxide gas.

11. Before step (2) and after step (1), pressurized gas is introduced into the mold cavity to reduce the pressure of the mold cavity.

(10) The method according to the above (9) or (10), wherein the pressure is such that the foamable molten resin injected in (2) does not cause foaming in the flow front.

1 2. Before the process (2), after the process (1), the mold cavity 12. The method according to the above item 11, wherein the pressurized gas introduced into the reactor is carbon dioxide gas.

13. The molten resin discharging means of the mold cavity is an open / close valve, and the mold has a molten resin discharge cavity that communicates with the mold cavity through the open / close valve. That is, the volume of the molten resin discharging cavity is larger than the volume of the foamed molten resin mass discharged to the outside of the mold cavity through the on-off valve in step (4). The method according to any one of the above items 9 to 12, which is characterized by the following.

14. The method according to the above item 13, wherein the molten resin discharging cavity has a ventilation hole communicating with the outside of the mold.

15. The foamable molten resin comprises the molten resin and at least one gaseous foaming agent dissolved therein, and the at least one gaseous foaming agent comprises carbon dioxide gas and nitrogen. 15. The method according to any one of items 9 to 14, wherein the method is selected from a group consisting of gas.

16. The method according to the above item 15, wherein the content of the foaming agent in the foamable molten resin is 0.05 to 10% by weight. As described above, the method of the present invention includes the step of (3) Do not use pressurized gas to pressurize the molten resin mass in the mold cavity

There are a first method (by applying a resin holding pressure, etc.) and a second method in which a pressurized gas is used to press the molten resin mass in the mold cavity in step (3). In the first method, the injection amount of the foamable molten resin in the step (2) is measured under a predetermined injection temperature and pressure condition and has the same volume as the volume of the mold cavity. It is in the range of 95 to 110% by weight of the foamable molten resin, preferably in the range of 98 to 105%. Further, in the second method, the injection amount of the foamable molten resin in the step (2) is measured under a predetermined injection temperature and pressure condition and has a volume equal to the volume of the mold cavity. It is in the range of 55 to 110%, preferably in the range of 60 to 100% by weight of the soluble molten resin. The reason that the injection amount of the foamable molten resin can exceed 100% of the weight of the foamable molten resin having the same volume as the mold cavity is that the molten resin is compressed by the injection pressure. Because it is done. The “injection temperature” in the present invention refers to a cylinder temperature of a molding machine and is substantially equal to a temperature of a molten resin to be injected. The “injection pressure” in the present invention is a pressure required to inject a molten resin. Hereinafter, the injection amount of the molten resin defined as above is hereinafter often referred to as “mold mold filling rate”.

Hereinafter, the present invention will be described in detail.

As a result of intensive studies by the present inventors to solve the problems of the prior art, a specific amount of carbon dioxide gas was dissolved in the molten resin. The carbon dioxide gas acts as both a plasticizer and a foaming agent only during molding, and the molded product after molding is not deformed and the carbon dioxide gas is released into the atmosphere, thus changing the resin performance. That the viscosity of the molten resin can be reduced, solidification can be suppressed, and foam injection molding can be easily performed.In addition, since the molten resin has high foamability, the mold surface state is transferred to the molded product. Even after the pressure is maintained, a part of the foamable molten resin mass wrapped in the skin layer is broken by the foaming pressure of the foamable molten resin mass itself. It has been found that the molten resin can be sufficiently discharged to the outside of the mold cavity through the molten resin discharging means. Also, since the part of the molten resin mass is discharged in a very short time, a rapid expansion can be generated while the molten resin is hardened, so that a high expansion ratio is achieved. It has been found that because the molten resin is rapidly cooled by the heat of vaporization at this time, the cooling time is short and the molding cycle can be shortened. Then, it was found that the obtained foamed molded article had a substantially non-foamed skin layer and a foamed layer wrapped by the skin layer, and was excellent in surface appearance and dimensional accuracy. Furthermore, the present inventors have also found that a similar effect can be obtained when a foaming gas (for example, nitrogen gas) other than carbon dioxide gas is used. Based on these findings, the present invention has been completed.

The method of the present invention lowers the solidification temperature by dissolving foaming gas typified by carbon dioxide gas in a molten resin, To improve the melt fluidity of the resin and to form a part of the foamable molten resin mass after pressing the foamable molten resin mass against the inner wall of the mold cavity by the injection pressure or high pressure gas. Due to the foaming pressure of the mold itself, the foam is discharged to the outside of the mold cavity through the molten resin discharge means to reduce the pressure on the foamed molten resin mass, thereby reducing the pressure in the mold cavity. This is a foam injection molding method that obtains a highly foamed molded product with excellent appearance and dimensional accuracy by combining foaming of the foamable molten resin mass.

That is, by dissolving a foaming gas such as carbon dioxide gas in the thermoplastic resin, at the same injection temperature, the viscosity of the molten resin is significantly lower than the inherent viscosity of the thermoplastic resin, and the solidification temperature is lowered. It lowers the fluidity and foamability. In this state, when the molten resin is injected and filled into the mold cavity by the counter pressure method, the molten resin is filled in a state in which foaming of the molten resin is suppressed by the pressurized gas in the mold cavity. . Further, when the molten resin is pressed against the mold surface while being pressurized, the viscosity of the molten resin is reduced by containing the foaming gas as described above, and the resin is filled with full shot. Or a high-pressure gas to form a gas-filled hollow portion, and because the gas pressure is maintained, it is strongly pressed against the inner wall surface of the mold cavity, and the inner wall surface of the mold cavity is pressed. The shape is well transferred to the surface of the molten resin mass. In the method of the present invention, only the surface portion of the molten resin mass is cooled and solidified at this stage to form a skin layer. This skin layer is It has a non-foaming or micro-foaming (expansion ratio of less than 1.01) filled with fat. Since foaming does not occur afterwards in the solidified skin layer, a high-quality molded product having no foaming pattern on the surface can be obtained by the method of the present invention. Also, the thickness of the skin layer can be easily controlled by adjusting the cooling and solidifying time. The cooling and solidifying time is usually preferably in the range of 0.1 second to 2 seconds.

At the stage where the skin layer is formed, the molten resin mass inside the skin layer is kept sufficiently foamable because the solidification temperature is lowered due to the dissolution of the foamable gas. ing. In the method of the present invention, a part of the molten resin mass is instantaneously discharged and released to the outside of the mold cavity through the molten resin discharging means by the foaming pressure of the molten resin mass itself, and is melted in the mold cavity. The resin mass is foamed, or at least a part of the molten resin mass and at least a part of the pressurized gas in the gas-filled hollow portion are subjected to the foaming pressure and the gas-filled hollow portion of the molten resin mass itself. The pressure of the pressurized gas instantaneously discharges and opens the outside of the mold cavity through the molten resin discharge means, and foams the molten resin mass in the mold cavity.

As described above, according to the method of the present invention, the thickness of the skin layer and the foaming ratio can be easily controlled. A molded article having a foaming ratio of 1.05 to 4.0 as the expansion ratio of the foamed layer can be favorably molded. Also, the thickness of the skin layer is not more than 20% of the maximum thickness of the molded article, or a thin skin layer having a thickness of 1 mm or less, and A lightweight molded article having a foamed layer having an open-cellular structure can be favorably molded.

Examples of the thermoplastic resin used in the molding method of the present invention include polyethylene, polypropylene, polyvinyl chloride, acryl resin, styrene resin, polyethylene terephthalate, and polyethylene terephthalate. Polybutylene terephthalate, polylaterate, polyphenylene ether, modified polyphenylene ether resin, wholly aromatic polyester, polyacetylene, polyphenylene ether, polyetherate -Thermoplastic plastics such as Louismid, Polyethersulfone, Polyamide resin, Polysulfone, Polyether terketone, Polyether terketone, etc. It is a material, a composition in which two or more of these are mixed, and various fillers are blended with them. The styrene-based resin used herein refers to homopolymers and copolymers that use styrene as an essential raw material, and polymer blends obtained from these polymers and other resins, and polystyrene. Or it is preferably ABS resin. Polystyrene is a styrene homopolymer. Further, a so-called rubber-reinforced polystyrene having a structure in which rubber is distributed in a polystyrene resin phase is also preferably used.

In particular, in the method of the present invention, a thermoplastic resin whose melt viscosity is greatly reduced when a foaming gas, particularly carbon dioxide gas is dissolved, is preferable, and a styrene-based thermoplastic resin is used for an amorphous thermoplastic resin. Resin, polycarbonate, polyphenylene ether, modified poly Phenylene ether resin is preferred. In particular, polycarbonate not only has high solubility of carbon dioxide, but also produces carbon dioxide when pyrolyzed. Therefore, decomposition reaction occurs when molten resin contains carbon dioxide gas as a blowing agent. This is advantageous for the method of the present invention, because it has the advantage that the equilibrium is shifted and the decomposition reaction rate is reduced. Further, among crystalline thermoplastic resins, a polyamide resin composition containing 10% by weight or more of an inorganic filler such as glass fiber is preferable. Those having an aromatic ring are particularly suitable.

In addition, in the method of the present invention, the molecular weight of various difficult-to-process resins, for example, the resin is too large to be injection-molded by a conventional method, or the amount of inorganic fillers is large, and the flowability is very poor. Additives such as thermoplastic resin, resin with poor thermal stability and easy to decompose, resin with high softening temperature that needs to be molded at a remarkably high temperature, and pyrolysis and flame retardant Resins can also be used by dissolving a large amount of foaming gas such as carbon dioxide

(The above-mentioned "large amount of foaming gas" means, for example, 0.2% by weight or more based on the sum of the foaming gas weight and the resin weight).

In the method of the present invention, it is generally used for extrusion molding, but a thermoplastic resin having low flowability for injection molding by a conventional method, or a thermoplastic resin having a molecular weight that is too large for injection molding by a conventional method. Resins, thermoplastic resins whose softening temperature is too high to be injection molded by conventional methods, also require large amounts of foaming gas (eg, foaming By dissolving 0.2% by weight or more with respect to the sum of gas weight and resin weight), it can be used favorably. The following thermoplastic resins are examples of these.

(1) Acrylic resin with a melt flow rate of 1.0 or less.

(2) Polystyrene with a melt rate of 1.5 or less.

(3) Rubber-reinforced polystyrene with a melt flow rate of 2.0 or less.

(4) ABS resin with a melt flow rate of 3.0 or less.

(5) Polycarbonate with a melt flow rate of 6.0 or less.

(6) A polyphenylene ether resin composition containing 60% by weight or more of polyphenylene ether or polyphenylene ether.

(7) Polyacetal with a merit of less than 5.0.

(8) Polyethylene with a mel flow rate of 5.0 or less.

(9) Polypropylene with a melt rate of 5.0 or less.

(10) A thermoplastic resin containing an easily decomposable flame retardant (for example, Mobifenyl ether, tribromophenol, chlorinated polyethylene).

Here, the meritlett rate is a value measured by the measurement method described in JISK7201, and the measurement conditions are the measurement conditions described in the JIS that are generally used for each resin. For acrylic resin, condition 15; for polystyrene and rubber-reinforced polystyrene, condition 8; for ABS resin, condition 11; and for poly-polycarbonate, condition 20. Here, the values of polyacetal and polyethylene are measured under condition 4, and the values of polypropylene are measured under condition 14; the unit is g / 10 minutes.

In general, the greater the molecular weight of the thermoplastic resin, the better the chemical resistance and impact resistance of the molded product, but the lower the fluidity during molding and the more difficult the injection molding. Extrusion does not require as high a fluidity as injection molding, so polymers of high molecular weight are commonly used and are used in the process of the present invention for these extrusions and not for injection molding The high-molecular-weight polymer also dissolves a large amount of carbon dioxide, and the molten resin mass itself has a part of the molten resin mass after the foamable molten resin mass is pressed against the mold wall surface by pressing. Due to the foaming pressure, the molten resin is discharged to the outside of the mold cavity through the molten resin discharging means to reduce the pressure on the molten resin mass, thereby foaming the molten resin mass in the mold cavity. By using these in combination, it is possible to mold a foam molded article having a thin portion and excellent appearance.

Examples of thermoplastic resins whose softening temperature is too high for injection molding include poly (vinylene ether), poly (phenylene ether) and polystyrene, or rubber-reinforced polystyrene. And a weight mixing ratio of 100: 0 to 60:40. Polyethylene polyester has poor moldability, and is generally polystyrene or rubber reinforced poly. Tylene is used in an amount exceeding 40% by weight. However, according to the molding method of the present invention, even when the blending amount of polystyrene or rubber-reinforced polystyrene is 40% by weight or less, a large amount of foaming gas such as carbon dioxide is used. For example, it can be used by dissolving 0.2% by weight or more based on the sum of the foaming gas weight and the resin weight.

The method of the present invention is also effective for resins that decompose or degrade when heated until the molten resin has sufficient fluidity, such as a high softening temperature and a low decomposition temperature. Thus, high fluidity can be obtained at a low resin temperature. In general, when the thermoplastic resin is an amorphous thermoplastic resin, molding is performed at a temperature not higher than the glass transition temperature of the thermoplastic resin containing no foaming gas + 150 ° C as the melting temperature. When the thermoplastic resin is a crystalline thermoplastic resin, the melting temperature is not higher than the melting point of the thermoplastic resin containing no foaming gas + 100 ° C or less. Molding is possible.

The foaming gas (gas foaming agent) used by being dissolved in the thermoplastic resin in the present invention has an effect as a plasticizer that lowers the melt viscosity when dissolved in the thermoplastic resin. There is no particular limitation, as long as it is soluble in thermoplastic resin, it does not degrade resin, molds and molding machine materials, has no environmental dangers, and is inexpensive. Further, it is preferable to use a material that satisfies restrictions such as rapid volatilization from a molded product after molding. Examples of the gaseous foaming agent include replacing some of the hydrogen atoms of carbon dioxide gas, nitrogen gas, saturated hydrocarbons having 1 to 5 carbon atoms, and saturated hydrocarbons having 1 to 5 carbon atoms with fluorine. Fluoroalkane obtained by the above method, for example, fluorocarbon. Of these, carbon dioxide gas and nitrogen gas are preferred, and carbon dioxide gas is most preferred. Nitrogen gas has lower solubility in resin than carbon dioxide gas and has less plasticizer effect, but it has a temperature characteristic of increasing solubility in resin at higher temperatures, so it can obtain a high foaming pressure. it can.

In addition, since it is difficult to directly measure the content of the foaming gas (gaseous foaming agent) in the foaming molten resin injected into the mold cavity, in the present invention, the weight of the molded article immediately after the injection molding is reduced. Leave the molded article in a hot air dryer at a temperature below the glass transition temperature for amorphous resin for 24 hours or more, or about 30 ° C above the melting point for crystalline resin. Leaving in a low-temperature hot air dryer for 24 hours or more, the difference in the weight of the molded product, in which the amount of foaming gas contained in the molded product was dissipated, was injected into the mold cavity to generate the foamed molten resin. The content of foaming gas was used. The amount of effervescent gas that escapes during injection molding differs slightly depending on the molding method. In particular, a preferred embodiment of the present invention is to use carbon dioxide gas for effervescent gas and pressurize gas for pressurizing the mold cavity. When molding by the counter-press method using carbon dioxide gas, the amount of foaming gas in the molded article immediately after molding, that is, the amount of carbon dioxide gas, is used in the foaming molten resin. There is almost no difference in the content of effervescent gas (carbon dioxide).

The foaming gas, particularly the carbon dioxide gas, dissolves well in the thermoplastic resin, becomes a good plasticizer, improves the fluidity of the thermoplastic resin, and functions as a foaming agent. The foamable molten resin used in the method of the present invention comprises the molten resin and at least one gaseous blowing agent dissolved therein. In the present invention, the content of the gaseous foaming agent in the foamable molten resin is preferably in the range of 0.55% by weight to 10% by weight. When the content is 0.05% by weight or more, the melt fluidity of the resin can be remarkably improved and the resin can be foamed, more preferably 0.2% by weight or more, and still more preferably 0.2% by weight. More than 5% by weight. Further, it is desirable that the maximum content of the gaseous foaming agent in the foamable molten resin is about 10% by weight. This is because the dissolution of a gaseous blowing agent (especially carbon dioxide gas) in a large amount into the molten resin is subject to many restrictions on equipment, and the counter gas pressure required when molding by the counterpressing method. This is because the pressure (pressure at which the mold cavity is pre-pressed with the pressurized gas before the injection of the molten resin) becomes extremely high. The content of the gaseous blowing agent in the foamable molten resin is preferably 7% by weight or less, and more preferably 5% by weight or less. In order to increase the foaming ratio of the molded article, it is necessary to increase the amount of the gaseous blowing agent (eg, carbon dioxide) dissolved in the foamable molten resin to lower the viscosity of the molten resin and to enhance the foaming property of the molten resin. Is preferred. The following two methods are preferred as a method for dissolving a foaming gas (gaseous foaming agent) in a thermoplastic resin. Here, a case where carbon dioxide gas is used as the foaming gas will be described as an example.

The first is a method in which granular or powdery resin is absorbed in advance in a carbon dioxide gas atmosphere and then supplied to the injection molding machine.It is absorbed by the pressure, ambient temperature, and time of absorption of carbon dioxide. The amount is determined. For example, if the pressure of carbon dioxide gas is 2 to 10 MPa and the resin is absorbed at room temperature for 3 to 8 hours, the content of carbon dioxide gas in the resin becomes 0.1 to 10% by weight. In this method, a part of the carbon dioxide gas in the resin is volatilized as the resin is heated during plasticization, so that the amount of the carbon dioxide gas in the molten resin is smaller than the amount previously absorbed. For this reason, it is desirable that the resin supply path, such as the hopper of the molding machine, also be a carbon dioxide gas atmosphere.

Another method is to dissolve carbon dioxide gas in the resin during or after plasticizing the resin in the molding machine cylinder. In addition, carbon dioxide gas is injected into the plasticized resin from the middle, tip, or cylinder of the screw. When injecting carbon dioxide gas from the middle of the screw cylinder, it is preferable to increase the screw groove depth near the injection part to lower the resin pressure. Also, after injecting carbon dioxide gas, it is uniformly dissolved and dispersed in the resin. For this reason, it is preferable to provide a mixing mechanism such as a damage or a mixing pin to the screw or to provide a static mixer in the resin flow path. As the injection molding machine, either an in-line screw system or a screw pre-blur system (using a ram type injection molding machine with a screw pre-plasticizing device) can be used. It is particularly preferable because it is easy to change the screw design of the extruder part for plasticizing the resin and the injection position of carbon dioxide.

The carbon dioxide gas in the thermoplastic resin is gradually released into the atmosphere if the molded article is left in the air after the thermoplastic resin has solidified.

In the method of the present invention, a pressurized gas is introduced into the mold cavity before the step (2) (injection of the molten resin), and the pressure of the mold cavity is injected in the step (2). In order to obtain a good appearance, it is preferable to set the pressure so that the foamable molten resin does not cause foaming at the flow front, that is, to perform injection molding by a coupon prestressing method. No. The “pressure at which the foamable molten resin injected in step (2) does not cause foaming in the flow front” (pressure of the pressurized gas introduced into the cavity) is defined as the foamable molten resin. It is usually 3 PMa to 10 PMa, preferably 5 PMa to 8 PMa, although it varies depending on the foaming pressure of the compound. The pressure of the pressurized gas introduced into the cavity only needs to be a minimum pressure that does not cause a foaming pattern on the surface of the molded product.The amount of gas used in one process should be minimized, and the sealing of the mold cavity can be performed. Simple structure of gas supply device For simplicity, it is better to keep the gas pressure close to the minimum required.

As the gas to be injected into the mold cavity by the counter-plate method, air, carbon dioxide gas, nitrogen gas, and other various gases that are inert to the resin can be used alone or as a mixture. Gases with high solubility in thermoplastic resins, e.g., carbon dioxide gas, nitrogen gas, part of hydrogen atoms in saturated hydrocarbons having 1 to 5 carbon atoms, and saturated hydrocarbons having 1 to 5 carbon atoms Fluoroalkanes obtained by substituting with fluorine, for example, freon, are preferred. Carbon dioxide gas is particularly preferred because it has a high effect of improving the transferability of the inner wall surface of the mold cavity to the molded product. In a case where an amorphous resin is used as the resin and the mold cavity is pressurized with carbon dioxide gas before the injection of the molten resin, the present inventors have already disclosed in Japanese Patent Application Laid-Open No. H10-1288783. (Corresponding to EP826477A2) and Japanese Patent Application Laid-Open No. 11-245562, as described in Japanese Patent Application Laid-Open No. 11-245562, the higher the pressure inside the capty, the better the transferability. Therefore, when high transferability is required, it is preferable to increase the gas pressure according to the clamping force of the molding machine and the sealing performance of the mold. The carbon dioxide content of the pressurized gas introduced into the mold cavity is preferably higher, and particularly preferably 80% by weight or more.

In the method of the present invention, preferably, the molten resin is not foamed after the molten resin is injected and filled into the gas-pressurized mold cavity. The molten resin is pressed against the inner wall surface of the mold cavity with high pressure, and the surface shape of the inner wall surface of the mold cavity is transferred to the molten resin mass. Hold until layer has formed. The pressurized gas supplied into the mold cavity before injection molding of the molten resin is checked whether there is a swirl mark on the surface of the molded product and the transfer status of the inner surface of the mold cavity. After the completion of resin injection and filling, select an appropriate time until the end of resin pressurization and open. If pressurized gas remains in the mold cavity after resin pressurization, the resin surface is pressed by the pressurized gas, causing dents or whitish surfaces due to foaming. It is not desirable.

In a preferred embodiment of the method of the present invention, a foamed molded article having no swirl mark on the molded article surface can be obtained by the counter-pressure method, but particularly for internal mechanism parts that do not require a good appearance. Can be formed without using the counter-pressure method. In this case, swirl marks are formed on the surface, but in step (3), pressure is applied to the molten resin mass by applying a resin holding pressure. It has a high skin layer, and it is possible to obtain light molded products with high foam and high strength and dimensional accuracy.

Also, using a sandwich molding method, injection-filling a non-foamable molten resin, injection-filling a foamable molten resin, forming a foamed layer, and foaming between the non-foamed layers Layer is Sandy In the case of manufacturing a molded product with a punched structure, there is no need for the counter pressure method.

In addition, as a method of pressurizing the molten resin mass in step (3) of the method of the present invention, a method of injecting additional molten resin into the mold cavity to apply a resin holding pressure, Injecting a pressure fluid such as gas into the molten resin, and injection compression molding to reduce the cavity volume. The pressure for pressurizing the molten resin mass is set so that the surface of the molten resin is pressed against the inner wall surface of the mold cavity and solidifies while sufficiently transferring the surface shape of the inner wall surface of the mold cavity. In particular, when carbon dioxide is used as the pressurized gas of the mold cavity, higher transfer pressure can be obtained with higher pressure. The pressure for pressurizing the molten resin mass is usually adjusted in the range of several MPa to 200 MPa according to the flow characteristics of the molten resin. The time required for pressurizing the molten resin mass is the minimum time required for the surface of the molten resin to solidify. If it is too long, the thickness of the molten portion to be foamed later decreases, or the resin temperature decreases and the viscosity increases. Therefore, it is difficult to obtain a sufficient foaming state. The pressurization time for the molten resin mass is usually in the range of 0.1 to 2 seconds.

As shown in Japanese Patent Application Laid-Open No. H11-124,556, when the mold cavity is pressurized with carbon dioxide gas and then filled with molten resin, the molten resin is cooled in the mold. In the filling process, carbon dioxide was dissolved in the molten resin during the filling process. At a mold temperature that is at least 35 ° C lower than the solidification temperature of the molten resin surface that has dropped, and at a mold temperature that is at most 5 ° C lower than the inherent solidification temperature of the thermoplastic resin. By cooling, the surface shape of the inner wall of the mold cavity can be highly transferred to the surface of the molten resin mass.

In the case where the molten resin mass is pressurized by injecting a pressure fluid such as a pressurized gas into the molten resin mass, the gas used to form the gas filling space is as follows. In the present invention, the same gas as the gas that can be used as a gas that can be used as a foaming gas (a gaseous foaming agent) to be contained in a molten resin or a gas for pressurizing a mold cavity in advance can be used. The same gas may be used as the gas for forming the hollow portion, the gaseous foaming agent, and the pressurized gas for the mold cavity, but it is not always necessary to use the same gas, and any combination is possible. As the pressurized gas that forms the hollow portion, carbon dioxide gas is used because of its excellent effect of lowering the glass transition temperature (Tg) and solidification temperature of the molten resin and its excellent solubility in the molten resin. I like it

Further, according to the present invention, after the molten resin is once full-shortened, a part of the molten resin mass is discharged to the outside of the mold cavity (for example, the resin discharging cavity 3) to reduce the pressure on the molten resin mass. Since a foam layer is formed by lowering the temperature, it is necessary to mold two or more foam molded products at the same time with one mold or to obtain two or more foam molded products with different volumes with one mold. The expansion ratio of the molded product Uniformity can be easily obtained, and multi-cavity molding can be easily performed.

Hereinafter, the present invention will be further described with reference to the drawings.

FIGS. 1 (a) to 1 (c) are explanatory views schematically showing one example of an embodiment of the first method of the present invention in a case where the obtained molded article has a thick rod shape. is there.

In Figs. 1 (a) to 1 (c), reference numeral 1 denotes a mold composed of a fixed half mold la and a movable half mold lb, and the inner wall of the fixed half mold la and the inner wall of the movable half mold lb. Thus, a mold cavity 2 and a resin discharge cavity 3 are formed. The mold cavity 2 is a space in the mold 1 for molding a molded product. The resin discharge cavity 3 outside the mold cavity 2 is a space in the mold 1 which is not intended for molding a molded product as a product, and is a space in the mold cavity 2. And a communication passage 5 which is opened and closed by an on-off valve 4 (melt resin discharging means). As the on-off valve 4, a valve that opens and closes by hydraulic pressure, air pressure, magnetism, motor, or the like can be used. Reference numeral 12 denotes an injection nozzle, and reference numeral 13 denotes a pressurized gas nozzle built in the injection nozzle 12. In addition, the resin discharge cavity 3 has a gas supply port 14 and a vent 14 serving as a discharge port, and the vent 14 is connected to the counter gas supply three-way valve 16 by piping. Have been. In addition, a gas injection port 18 is provided to allow the pressurized gas to be directly injected into the molten resin mass in the mold cavity 2. You.

First, as shown in FIGS. 1 (a) and 1 (b), with the on-off valve 4 closed, the foaming molten resin 8 is injected from the injection nozzle 12 into the mold cavity 2. To form a molten resin mass in cavity 2. The foamable molten resin 8 is to be injected and filled into the mold capty 2 through the sprue 6 and the runner 17. In this embodiment, before injecting the foamable molten resin 8, a gas body is supplied from the counter gas supply hole 14 to pressurize the mold cavity 2, and then the gas is supplied to the thermoplastic resin. The foaming molten resin 8 containing a foaming agent (for example, carbon dioxide gas) is injected and filled into the mold cavity 2 from the injection nozzle 12. The mold cavity filling rate of the molten resin 8 is in the range of 95% to 110%.

Immediately before or immediately after resin filling is completed, pressurized gas in the mold cavity 2 is connected to the vent 14 of the cavity 3 for resin discharge. And immediately release to the atmosphere. When the on-off valve 4 is closed, molten resin cannot pass through, but is not airtight and gas can pass. Unless the counter pressurized gas in the mold cavity 2 is released, the gas pressure in the mold becomes high as the resin is filled, and resin filling failure occurs at the end of the mold cavity 2, etc. Alternatively, since a large amount of gas is absorbed on the resin surface, an unfavorable phenomenon such as whitening due to foaming occurs on the resin surface. Then, by injecting additional molten resin into the molten resin mass and maintaining the same for a predetermined time while applying pressure, the surface of the molten resin mass 8 that is in contact with the inner wall surface of the mold cavity is cooled and solidified, so that substantially no molten resin is formed. A foamed skin layer 10 is formed. If the cooling and solidifying time is lengthened, the skin layer becomes thicker.

Then, as shown in FIG. 1 (c), when the on-off valve 4 communicating with the resin discharge cavity 3 from the mold cavity 2 is opened, the molten resin mass 8 wrapped in the skin layer 10 itself is opened. Due to the foaming pressure of the molten resin, a part of the molten resin mass and the foaming gas volatilized from the molten resin are discharged to the molten resin discharge cavity 3 through the communication passage 5, so that the molten resin in the mold cavity 2 is melted. The volume of the resin mass 8 decreases, and the pressure on the molten resin mass 8 decreases, whereby a foam layer 9 is formed.

During the formation of the foam layer 9, a part of the molten resin mass 8 breaks a part of the skin layer 10 and is discharged to the molten resin discharge cavity 3, so that the skin layer 10 is thin enough not to hinder this. It is preferable to form it. From this viewpoint, the thickness of the skin layer 10 is usually preferably about 0.1 mm to 1 mm.

In order to break the skin layer 10, it is also effective to open the on-off valve 4 and then press the molten resin mass 8 by injecting additional molten resin. The volume of the resin discharge cavity 3 is set so that the part of the molten resin mass discharged to the outside of the mold cavity 2 by the foaming pressure of the foamable molten resin mass 8 is not densely filled. It is preferable to set the volume to be larger than the volume of the part of the molten resin mass to be discharged, and it is further preferable to make the volume of the resin discharge cavity 3 as large as possible.

As described above, the resin discharging cavity 3 is not completely filled with the molten resin, or the molten resin discharging cavity 3 is provided with the vent 14. The problem of instantaneous release of the counter gas, air, and foam gas in the mold can be prevented, and it takes time to depressurize and a sufficient foaming state cannot be obtained. Problems such as insufficient conversion can be prevented.

2 (a) to 2 (c) are explanatory views schematically showing one example of an embodiment of the second method of the present invention in a case where the obtained molded article is in the form of a thick rod. .

In the embodiment shown in FIGS. 2 (a) to 2 (c), after filling about 70% of the volume of the mold cavity 2 with the foamable molten resin 8, the molten resin mass 8 A pressurized gas having a pressure capable of suppressing foaming of the molten resin mass is injected to form a hollow portion 11 filled with the pressurized gas. The injection of the pressurized gas in this example is performed from the pressurized gas nozzle 13 built in the injection nozzle 12, and, like the molten resin 8, the sprue 16 and the runner 7 are used. Then, it is injected into the molten resin mass 8 in the mold cavity 2. In addition to the pressurized gas nozzle 13, the pressurized gas injection port as shown in FIG. The mouth 18 may be provided directly near the gate of the mold cavity. As described above, the mold cavity 2 is filled with the molten resin 8 having the hollow portion 11 filled with the pressurized gas, and the skin layer 1 is maintained for a predetermined time while maintaining the injection pressure of the pressurized gas. Form a 0. Next, close the valve (not shown) that controls the injection of the pressurized gas, or open the on-off valve 4 while keeping the above valve open. Then, out of the skin layer 10 surrounding the gas-filled hollow portion 11, the skin layer 10 near the communication passage 5 is located between the gas-filled hollow portion 11 and the molten resin discharge cavity 3. The molten resin is discharged by the molten resin discharge cavity 3 due to the pressure difference between the two, and the pressurized gas in the hollow portion 11 passes through the molten resin discharge cavity 3 and is quickly released from the ventilation port 14. You. As a result, the pressure in the hollow portion 11 drops sharply, and the foaming of the molten resin 8, which has been suppressed by the pressure of the pressurized gas in the hollow portion 11, occurs around the hollow portion 11. Part of the generated and foamed molten resin and the foaming gas volatilized from the molten resin are also discharged to the molten resin discharge cavity 3, and as shown in FIG. 2 (c), the inside of the hollow portion 11 is formed. And the surrounding area becomes a foamed layer 9. Sudden pressure reduction in the hollow portion 11 uses the on-off valve 4 that leads to the molten resin discharge cavity 3 as described above, and also, for example, an injection needle that can advance and retreat with respect to the mold cavity 2. A hollow pin (not shown) is placed in the mold, and the pin is pierced into the molten resin mass formed with the hollow portion 11, and the pin in the hollow portion 11 is inserted through the hole of the pin. Pressurized gas to gold It can also be done by releasing it out of mold 1. The volume of the molten resin discharge cavity 3 is preferably set to a volume that is not densely filled with the molten resin extruded by the gas pressure forming the hollow portion 11 or the molten resin extruded by foaming. Preferably, gas is discharged from the molten resin discharge cavity 3 to the outside of the mold instantaneously. The mold cavity filling rate of the molten resin 8 can be arbitrarily set in the range of 55% to 110%.

Considering that the molten resin discharging cavity 3 is not completely filled with the molten resin, or by providing the molten resin discharging cavity 3 with a vent 14, the hollow portion can be formed. It is possible to prevent the problem that the pressurized gas to be formed is not sufficiently released and the problem that the decompression takes time and a sufficient foaming state cannot be obtained, and the product cannot be reduced in weight sufficiently.

As described above, the carbon dioxide gas is preferably used as the pressurized gas for forming the hollow portion. When carbon dioxide gas is used, even if the holding time after injection of the pressurized gas is lengthened, the carbon dioxide gas is further absorbed from the gas-filled hollow portion 11 into the surrounding molten resin, so that the molten resin When the solidification is suppressed, a good foaming state is easily obtained.

In addition, carbon dioxide gas is used for the gas forming the hollow portion 11, and the supply of the gas forming the hollow portion 11 is continued even after the on-off valve 4 is opened, and is provided in the molten resin discharge cavity 3. Vent 1 4 By opening the molded product outside the mold, the inside of the foamed molded product is cooled by the adiabatic expansion of the carbon dioxide gas. This makes it possible to shorten the cooling and solidifying time after step (4) of the method of the present invention. Even if the mold temperature is raised above the glass transition temperature (Tg) of amorphous resin and the temperature of crystalline resin is raised to near the melting point, it is possible to take out molded products and the appearance is extremely good. A molded product can be obtained.

After the above foaming, the foamed resin mass having a substantially non-foamed skin layer in the mold cavity 2 is cooled to a temperature at which it can be taken out, and the mold 1 is opened to take out a molded product. The molded article obtained is non-foamed because the skin layer 10 is cooled to a temperature at which foaming does not occur before foaming, and the inner layer is a foamed layer 9 due to the foaming.

In both the first method and the second method of the present invention, the mold cavity is pressurized with a gas beforehand in order to eliminate the possibility of appearance defects such as silver on the skin layer of the molded article. Is preferred (counter pres- sure method).

In the case of using the counter pressure method, it is preferable to use a mold in which the periphery of the mold cavity is sealed in order to easily obtain a necessary counter gas pressure. For example, in the mold 1 shown in FIGS. 1 (a) to 3 (c), a single ring 15a to 15c for sealing each gap in the mold leading to the mold cavity 2 is provided. It is provided. Therefore, in one example of the first method described above, After the counter gas is supplied from the counter gas supply hole 14 to fill the inside of the mold 2 with the counter gas, the foaming molten resin is injected and filled, thereby preventing foaming of the molten resin at the time of injection. It can be easily suppressed. In addition, the counter gas supply hole 14 can be opened as a slit or small hole or a porous shape that does not allow molten resin to enter, so that the mold cavity 2 can be directly opened. It can also be opened at the end. · '

3 (a) to 3 (d) show an example of an embodiment of the second method of the present invention in a case where the obtained molded product has a shape having a thick portion on one side of a large thin portion. FIG. With the on-off valve 4 closed, the molten resin 8 is injected into the mold cavity 2 from the injection nozzle 12. The molten resin 8 is injected and filled through the sprue 6 and the runner 7 into the thick part forming area and the thin part forming area of the mold cavity 2.

In the present invention, since the melt viscosity of the molten resin 8 is reduced by the foaming gas (gaseous blowing agent) (for example, carbon dioxide gas), the thin portion is quickly filled with the molten resin 8. If the mold cavity 2 is pressurized with pressurized gas before injection filling, the pressurized gas in the mold cavity 2 is discharged immediately before or immediately after resin filling is completed. Force connected to the ventilation port 14 of the bitty 3 ゥ Open the gas supply three-way valve 16 (not shown) and immediately open to the atmosphere.

In this embodiment, mold cavity filling with molten resin The rate is preferably between 95% and 110%, and more preferably between 98% and: L0.5%.

After injecting the foamable molten resin 8 into the mold cavity, a pressurized gas is injected into the molten resin mass 8 at a pressure capable of suppressing foaming of the molten resin, and the hollow portion filled with the pressurized gas is injected. Form 1 1. The injection of the pressurized gas in this example is performed from the pressurized gas nozzle 13 built in the injection nozzle 12 and, like the molten resin, passes through the sprue 6 and the runner 7. It is injected into the molten resin mass 8 in the mold cavity 2. The injection of the pressurized gas is performed to compensate for the cooling shrinkage of the molten resin mass 8 in the mold cavity 2, and in the molding of a molded product having a thick portion as in this example. As shown in Fig. 3 (c), the injection is focused on the thick part forming region. The thick portion is arranged continuously from the vicinity of the resin gate to the end of the flow of the resin, and is connected to the communication passage 5 to the molten resin discharge cavity 3.

In addition to the pressurized gas nozzle 13, the injection port of the pressurized gas may be provided directly at the thick portion or near the thick portion of the mold cavity. In this case, the injection port of the pressurized gas is preferably provided on the side opposite to the communication passage 5 to the molten resin discharge cavity 3. The thickness of the thick portion is set to 1.5 to 4 times the thickness of the thin portion so that the flow front preferentially flows through the thick portion when the molten resin is filled. I prefer to do that. As described above, the molten resin mass 8 is pressed against the inner wall surface of the mold cavity 2 by the hollow portion 11 filled with the pressurized gas, and is kept in this state for a predetermined time to form the skin layer 10. Next, the on-off valve 4 is opened. Then, a part of the skin layer 10 of the molten resin surrounding the gas-filled hollow portion 11 is broken by the pressure difference between the gas-filled hollow portion 11 and the molten resin discharge cavity 3, and the molten resin The oil in the cavity 11 is blown off to the side of the grease discharge cavity 3, and the pressure in the hollow portion 11 drops sharply, and the foaming of the molten resin 8 that was previously held down by the pressure of the pressurized gas in the hollow portion 11 Some of the foamed molten resin generated around the hollow portion 11 and foaming gas volatilized from the molten resin is also discharged to the molten resin discharge cavity 3, as shown in Fig. 3 (d). Then, the foamed layer 9 in and around the hollow portion 11 becomes foamed. It is also possible to discharge and foam a part of the molten resin into the molten resin discharge cavity 3 only by the foaming pressure of the molten resin 8 without forming the gas-filled hollow portion 11.

FIG. 4 is a schematic front view of a movable half mold of one example of a mold having four grip-shaped molded products, which can be used in the method of the present invention. As shown, in addition to the cavity 2, a resin discharge cavity 3, an on-off valve 4, and a gas inlet 18 for forming a gas-filled hollow portion are provided. Each gas inlet 18 is independently controlled so that the gas pressure does not interfere with each other. With the on-off valve 4 closed, the inside of each mold cavity 2 from the injection nozzle 12 is filled with molten resin. The molten resin 8 is to be injected and filled into the mold cavity 2 through the sprue 6 and the runner 7.

If the volumes of the cavities 2 are the same, it is preferable to set the runner and gate dimensions connected to the cavities 2 so that the molten resin is evenly filled in the cavities 2. New

If the runner length changes due to the arrangement of the cavities 2 or if the cavities have different volumes, the runner length and thickness are adjusted so that the resin filling completion timing for each cavity is the same. It is preferable to adjust the gate dimensions.

The gas inlets 18 are provided near the gates of the cavities, and the pipes connected to the gas inlets are preferably of equal length so that the gas pressure loss is equal. .

First, the molten resin 8 is injected and filled from the injection nozzle 12 into each mold cavity 2, and the molten resin mass is held for a predetermined time while being pressurized to form a skin layer 10. When 4 is opened, a part of the molten resin mass and the foaming gas are discharged to the molten resin discharge cavity 3 through the communication passage 5 due to the foaming pressure of the molten resin mass 8 wrapped in the skin layer 10. As a result, a foam layer 9 is formed in the molten resin mass 8 in the mold cavity 2. Once each cavity is completely filled and the resin is discharged to the molten resin discharging cavity 3 by the foaming pressure of the molten resin, the molded product of each cavity is It has the same appearance and foam layer.

In this example, after filling the molten resin, a hollow is formed by gas; if all the cavities 2 are filled with the molten resin, a gas is injected into the molten resin mass to form a hollow portion. After that, the supply of gas is stopped, and then the on-off valve 4 is opened to discharge a part of the molten resin and the gas in the hollow part to the molten resin discharging cavity 3 to form the foam layer 9. When the mold cavity filling rate of molten resin is relatively small, about 70%, and when forming a gas-filled hollow part in a short shot, the mold cavity filling rate is between the cavities. Particular attention must be paid to the length, cross-sectional dimensions, gate dimensions, gas piping length, etc. of the runners connected to each cavity so that they are evenly distributed.

In addition, when the foaming gas generated from the molten resin may cause defects such as silver appearance in the appearance, it is preferable to use the counter pressure method.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the effects of the present invention will be described more specifically with reference to examples.

Molding was performed using an injection molding apparatus as shown in FIG. 5. In FIG. 5, the injection molding machine 23 used was “SG260MS—S” manufactured by Sumitomo Heavy Industries, Japan. The screw cylinder 20 of the injection molding machine has nine vent types, and the vent part can be pressurized with carbon dioxide gas. By keeping the pressure of the carbon dioxide gas or nitrogen gas supplied from the carbon dioxide gas source 24 or nitrogen gas source 24 via the gas supply control device 19 constant by the pressure reducing valve, the carbon dioxide dissolved in the molten resin The amount of carbon gas or nitrogen gas was controlled. From the time of plasticization to the start of injection, a minimum pressure was set and maintained as the screw back pressure so that the molten resin did not foam and the screw receded.

The mold 1 can be supplied with carbon dioxide gas or nitrogen gas from a carbon dioxide gas source 24 or a nitrogen gas source 24 via a gas supply control device 19 and a counter gas supply line 22. The sea is falling. Example 1

A rod-shaped molded product having a cross section of approximately 20 mm X 20 mm and a length of 300 mm was formed by the method shown in Figs. 1 (a) to 1 (c). Mold 1 has a cross-section at one end of a rod-shaped mold cavity 2. A 5 mm X 10 mm gate is provided, and a communication passage 5 with a cross section of 5 mm X 10 mm and a length of 15 mm is provided at the end opposite to the gate, and a hydraulic pressure is applied to the center of the communication passage 5. An on-off valve 4 for opening and closing is provided, and a molten resin discharge cavity 3 having a cross section of 20 mm × 20 mm and a length of 600 mm is connected to the end of the communication passage 5.

8 MPa of carbon dioxide is supplied from an injection cylinder to a polyamide 66 (Rona (registered trademark) 1442 G, manufactured by Asahi Kasei, Japan) containing 33% of glass fiber, and dissolved while melting. Injection molding was performed as shown in Fig. 1 (a) and Fig. 1 (b). The cylinder temperature was 280 ° C and the injection pressure was 120 MPa. The mold cavity filling rate of the molten resin was 100%. First, the mold 1 is closed, the injection nozzle 12 is pressed into contact with the mold 1, and then the carbon dioxide gas with a pressure of 7 MPa is supplied from the counter gas supply hole 14 for 3 seconds to pressurize the mold. Cavity 2 (mold temperature: 80 ° C.) was filled with the above glass fiber-containing polyamide resin (foamable molten resin) in which carbon dioxide gas was dissolved in 1.5 seconds. Immediately after filling is completed, the counter gas pressure is released to the outside through the molten resin discharge cavity 3 and the counter gas supply hole 14 (vent), and the resin pressure in the cylinder is 90 MPa for 3 seconds. After maintaining the pressure, the on-off valve 4 of the communication passage 5 is opened, and a part of the molten resin mass 8 is discharged to the molten resin discharging cavity 3 by the foaming pressure of the molten resin mass 8 itself. The pressure on the molten resin mass 8 was reduced to cause foaming. Molded product obtained by opening mold 1 60 seconds after foaming Removed. Thus, a molded article having a substantially non-foamed skin layer 10 and having a highly foamed foam layer inside was obtained.

'The amount of carbon dioxide gas in the foamable molten resin determined from the weight loss of the molded article after molding was about 1.0% by weight. The foaming ratio of the molded article was 1.4 times, and the thickness of the skin layer was about 1 mm. Example 2

The operation was performed in the same manner as in Example 1 except that the conditions were changed as follows. After setting the mold cavity filling rate to 70% and completing the injection of the foamable molten resin, the molten resin mass 8 is supplied with 8 MPa of carbon dioxide gas from the gas injection port 13 built into the injection nozzle 12. At the same time as forming the gas-filled hollow portion 11 by opening the inside, the counter gas in the mold cavity 2 is released, and the injection of carbon dioxide gas into the molten resin mass 8 and the gas pressure After continuing for 2 seconds, the injection of carbon dioxide gas was stopped, and the on-off valve 4 leading to the molten resin discharge cavity 3 was opened to open the carbon dioxide gas in the hollow portion 11 of the molten resin mass 8 and the gas. A portion of the molten resin mass 8 that was extruded with the entrainment was discharged into the molten resin discharge cavity 3 at a stretch, and the molten resin mass 8 in the mold cavity 2 was foamed.

The amount of carbon dioxide gas in the foamable molten resin was about 1.0% by weight. The foaming ratio of the molded product was 2.0 times, which was much lighter than that of Example 1. Example 3

The operation was performed in the same manner as in Example 1 except that the conditions were changed as follows.

The mold cavity 2 had the same shape as that of the first embodiment, but the inner wall surface of the mold cavity 2 was formed as a sipo with an average roughness (R a) of 13.2 m. The average roughness (Ra) was measured with a Surfcom 57 OA (Surfcom 570A) manufactured by Tokyo Seimitsu Co., Ltd., Japan. (For the average roughness (R a), refer to the Mechanical Engineering Handbook, Revised 6th Edition (Japan, published by The Japan Society of Mechanical Engineers; 1977).)

While supplying carbon dioxide gas from the injection cylinder 20 to polystyrene (A & M Styrene ΓΑ & Μ Polystyrene (registered trademark) 6885, Japan) at 10 MPa and dissolving it, Injected into mold cavity 2 in the same manner as above.The cylinder temperature was set at 220 ° C and the injection pressure was set at 100 MPa.The mold cap pressurized to 7 MPa with carbon dioxide gas. The polystyrene (foamable molten resin) obtained by dissolving carbon dioxide gas in Viti 2 (mold temperature: 50 ° C) is filled in 1.5 seconds, and the resin pressure in the cylinder is increased by 80 MPa. After holding the pressure for 2 seconds, the on-off valve 4 of the communication passage 5 is opened, and a part of the molten resin mass 8 is discharged to the molten resin discharging cavity 3, thereby foaming the molten resin mass 8. After 60 seconds, mold 1 was opened and the resulting molded product was removed.

The amount of carbon dioxide gas in the foamable molten resin was 3% by weight. The foaming ratio of the molded product was 2.6 times, and the thickness of the skin layer was 1.5 mm. In addition, the surface of the molded product is transferred with a grain shape with an average roughness (R a) of 13.1 m, and high transferability is obtained, and the surface has surface defects such as uneven gloss and flow marks. Was not seen. Example 4

The operation was performed in the same manner as in Example 1 except that the conditions were changed as follows. Polyresin Ponate ("Pan Light (registered trademark) L1225", manufactured by Teijin Chemicals Japan Limited) was used as the resin. Cylinder temperature 300 ° C, Injection pressure 220 MPa, Mold temperature 80 ° C, CO2 gas supply pressure to cylinder 100 Pa, Cavity to mold cavity 2 The water pressure is 7 MPa. Fill the above-mentioned resin with carbon dioxide dissolved in 2 seconds, and immediately release the gas pressure of the counter to the outside immediately after the filling is completed, while maintaining the resin pressure in the cylinder at 180 MPa. After maintaining the pressure for 1 second, the opening and closing valve 4 of the communication passage 5 is opened, and a part of the molten resin mass 8 is discharged to the molten resin discharging capity 3 by the foaming pressure of the molten resin mass 8 itself. Then, the molten resin mass 8 was foamed. 60 seconds after foaming, mold 1 was opened and the molded product was removed. Thus, a molded article having a substantially non-foamed skin layer 10 and having a highly foamed foam layer inside was obtained.

The amount of carbon dioxide gas in the foamable molten resin is about 2.0% by weight. there were. The expansion ratio of the molded product was 1.4 times, and the thickness of the skin layer was about 2 mm. Example 5

The operation was performed in the same manner as in Example 1 except that the conditions were changed as follows. Semi-aromatic polyamide containing 33% by weight of glass fiber and having about 10% by weight of an aromatic ring component as a resin to slow down the crystallization rate (“Leona (registered trademark)” manufactured by Asahi Kasei in Japan) 9 0 G 3.

3)) was used. Cylinder temperature 280 ° C, injection pressure 120MPa, mold temperature 80 ° C, carbon dioxide gas supply pressure to cylinder 2MPa, counter pressure 2 to mold cavity Is not used. The above-mentioned glass fiber-containing semi-aromatic polyamide resin in which carbon dioxide gas is dissolved is filled in for 2 seconds, and the resin pressure in the cylinder is maintained at 80 λ4 Pa for 1 second. Was released and a part of the molten resin mass 8 was discharged to the molten resin discharge cavity 3 by the foaming pressure of the molten resin mass 8 itself, and the molten resin mass 8 was foamed. 60 seconds after foaming, mold 1 was opened and the molded product was removed. Thus, a molded article having a substantially non-foamed skin layer 10 and having a highly foamed foam layer inside was obtained.

The amount of carbon dioxide gas in the foamable molten resin was about 0.1% by weight. The foaming ratio of the molded product is 1.4 times, and the thickness of the skin layer is about 2 mm.

Due to the low crystallization speed of the resin, and in full shot By molding, no foaming pattern appeared on the appearance, and a high quality appearance was obtained. Example 6

The procedure was performed in the same manner as in Example 2 except that the conditions were changed as follows. As shown in Fig. 3 (a) to Fig. 3 (c), a piece of a 2.5mm thick flat plate (thin wall) has a channel (thick wall) with a cross section of 4mm x 4mm. A mold having a cavity with a design (thin plate-one channel design) was used. At this time, the filling rate of the mold cavity with the molten resin is 98%, and after the filling of the molten resin is completed, the pressurized gas nozzle 13 built into the injection nozzle 12 and the carbon dioxide of 8 MPa The gas is injected into the molten resin mass to form the gas-filled hollow portion 11, and at the same time, the counter gas in the mold cavity 2 is released to the outside, and carbon dioxide gas is injected for 2 seconds. After the gas pressure was maintained, the injection of carbon dioxide gas was stopped, the on-off valve 4 leading to the molten resin discharge cavity 3 was opened, and the carbon dioxide gas in the hollow portion 11 of the molten resin mass 8 was removed. A part of the molten resin mass 8 extruded with the gas was discharged to the molten resin discharging cavity 3 at a stretch, and the molten resin mass 8 in the mold cavity 2 was foamed.

The amount of carbon dioxide gas in the foamable molten resin was about 1.0% by weight. The expansion ratio of the molded product was 1.2 times, and a molded product in which not only the thick part but also the thin part was foamed was obtained. Example 7

Molding was carried out using a mold 1 of four cavities having a lip shape with a diameter of 222 mm and a distance between end rims of 180 mm as shown in FIG. The runner distance to each mold cavity 2 is set approximately equal. Each of the cavities 2 is provided with a molten resin discharging cavity 3 through a communication passage, and each of the communication passages has an on-off valve 4. The operation timing of each on-off valve 4 can be controlled independently. The volume of the molten resin discharge cavity 3 is about 70 C C, the outer diameter is set to 3 O mm, and the depth is set to 100 mm. The cross-sectional shape of the communication passage leading from the cavity 2 to the molten resin discharge cavity 3 is 5 mm X 5 mm, and the cross-sectional shape of the cavity outlet from the cavity 2 to the communication passage is 5 mm X 5 mm. It is. A gas injection port 18 for forming the hollow portion 11 is disposed immediately adjacent to the resin gate of each cavity 2. The gas injection timing, pressure, and gas retention time for each cavity 2 can be controlled independently.

Polypropylene ("Novatech (registered trademark) TX1977K", manufactured by Nippon Polychem, Japan) was used as the resin. Cylinder temperature 230 ° (: Injection pressure 120 MPa, mold temperature 80 ° C, carbon dioxide gas supply pressure to the cylinder was 10 MPa. Each cavity 2 Is pressurized to 7 MPa with carbon dioxide gas, and the mold cavities of each cavity 2 are filled to a filling rate of about 75%. The amount of fat injection was set, and the above-mentioned polypropylene resin in which carbon dioxide gas was dissolved was filled in 2 seconds. At this time, gas injection was started into the molten resin mass 1.5 seconds after the start of the injection of the foamable molten resin, a gas-filled hollow portion was formed, and the gas pressure was maintained for 3 seconds. As the gas that forms the space during gas filling, 8 MPa carbon dioxide gas was used. Next, each gas supply side valve was closed, and the on-off valve 4 communicating with the molten resin discharge cavity 3 was opened. As a result, the pressurized gas and a part of the molten resin mass in the hollow portion were discharged to the molten resin discharge cavity 3, and the molten resin mass in the mold cavity 2 was foamed. 30 seconds after foaming, the mold was opened and the molded product was removed. Thus, a molded article having a substantially non-foamed skin layer and having a highly foamed foam layer inside was obtained.

At the stage when the gas-filled hollow portion was formed in the molten resin mass, the length of the hollow portion varied up to 20 mm between each of the cavities 2.However, molding from each of the cavities 2 after foaming The foaming ratio (weight reduction ratio) of the product was almost 2.2 times, and the thickness of the skin layer was uniform at 2.5 mm.

The amount of carbon dioxide gas in the foamable molten resin was about 3.0% by weight. Example 8

Even after opening the on-off valve 4 leading to the molten resin discharge cavity 3, the supply of carbon dioxide gas with the gas-filled hollow part 1 The procedure was performed in the same manner as in Example 2 except that the carbon dioxide gas was discharged to the molten resin discharge cavity for 2 seconds, and then the mold 1 was immediately opened to remove the molded product. · The molded product has a non-foaming layer on the surface and an open-cell structure

structure) having been formed. The molded product surface temperature was 60 ° C., 20 ° C. lower than the mold surface temperature, and a cooling effect due to adiabatic expansion of carbon dioxide was recognized. The expansion ratio and the thickness of the skin layer of the molded product were almost the same as those in Example 2. Example 9

The mold cavity 2 is pressurized with 6 MPa of nitrogen gas, the injection cylinder 20 to 8 MPa of nitrogen gas is supplied to the molten resin, and the gas-filled hollow portion 11 is filled with 8 MPa of nitrogen gas. The procedure was performed in the same manner as in Example 2 except for the formation of. The obtained molded product had the same expansion ratio and appearance as those of Example 2. The nitrogen gas content in the foamable molten resin was about 0.8% by weight. Comparative Example 1

Without opening the on-off valve 4 provided in the communication passage 5 leading to the molten resin discharge capital 3, the carbon dioxide gas that formed the hollow portion 11 was injected from the pressurized gas nozzle 13 built in the injection nozzle 12. The procedure was the same as in Example 2, except that the release was attempted. The foamable molten resin filled in sprue 6 and runner 7 is foaming. However, the inside of the molded product was not foamed, and when the mold 1 was opened, the molded product burst. This is considered to be because the foamable molten resin filled in the sprue 16 and the runner 7 foams first, and the carbon dioxide gas in the gas-filled hollow portion 11 of the molten resin mass 8 cannot be released. Comparative Example 2

The procedure was performed in the same manner as in Example 2 except that the conditions were changed as follows. The length of the molten resin discharge capacitor 3 was set to 7 O mm, the volume was set to 28 CC, and the filling rate of the mold cavity with the molten resin was set to 98%. After filling the resin and injecting the pressurized gas, open the on-off valve 4 and discharge a part of the molten resin mass into the molten resin discharge cavity 3 by gas pressure.The hollow body with a hollow ratio of about 30% Was formed. At this time, the molten resin discharging cavity 3 was densely filled with the resin pressed by the gas pressure. Next, the carbon dioxide gas in which the hollow portion 11 was formed was released from the pressurized gas nozzle 13 built in the injection nozzle 12. The molten resin filled in sprue 1 and runner 7 was foamed, but was not foamed in the molded product, and the molded product burst when mold 1 was opened. This is considered to be because the molten resin in the sprue 16 and the runner 7 foamed first, and the carbon dioxide gas in the gas-filled hollow portion 11 of the molten resin mass 8 could not be released. Comparative Example 3

The same procedure was performed as in Comparative Example 2 except that the conditions were changed as follows. The pressurized gas forming the hollow portion 11 was directly injected from the gas injection port 18 provided in the mold cap 2. The gas in the hollow portion 11 was released from the same gas inlet 18. The vicinity of the gas inlet 18 was foamed, the inside of the molded product was not foamed, and when the mold 1 was opened, the molded product burst, and the result was the same as that of Comparative Example 2. Example 10

The procedure was performed in the same manner as in Example 3 except that nitrogen gas was used as the pressurized gas for pressurizing the mold cavity 2. Although the surface of the obtained molded product had no foaming pattern, the surface roughness was 5 to 8 im and did not sufficiently transfer the sipo shape. 3 was better.

The amount of nitrogen gas in the foamable molten resin was 3% by weight. The foaming ratio of the molded product was 2.6 times, and the thickness of the skin layer was 1.5 mm. Comparative Example 4

Example 3 was repeated except that the molten resin discharge cavity 3 was not used and the mold 1 was opened after 60 seconds of cooling time after injection and the molded product was removed. The molded product removed from the mold swells greatly due to the foaming force of the gaseous foaming agent dissolved in the molten resin, Deformed. In order to prevent this deformation, a cooling time of more than 120 seconds was required. Comparative Example 5

Molding cavity 2 was not pressurized with a pressurized gas, and the filling was performed in the same manner as in Comparative Example 4 except that the mold cavity filling rate of the molten resin was 8.0%. Although a molded product with an expansion ratio of 1.2 times was obtained, a foamed pattern was formed on the surface of the molded product, and the appearance was poor. Comparative Example 6

In order to improve the appearance of the molded product, the procedure was performed in the same manner as in Comparative Example 5 except that the mold cavity 2 was pressurized with 7 MPa of carbon dioxide gas before the injection of the molten resin. The resulting molded product has no foaming pattern from the gate side in the mold cavity 2 to the point corresponding to the cavity volume of about 80% ', but from there it corresponds to the flow end. The appearance was poor due to the formation of a foam pattern toward the minute.

Industrial applicability

According to the foam injection molding method of the present invention, the mold cavity has good transferability of the inner wall surface shape, and a molded article having a non-foamed skin layer and a highly foamed foam layer is reproducible, efficient, and economical. In addition to being able to manufacture the molded product, the thickness of the skin layer of the molded product and the expansion ratio of the molded product can be easily controlled. ADVANTAGE OF THE INVENTION According to the foam injection molding method of this invention, various excellent thermoplastic resin foam injection molded articles, such as housing of light electric equipment and electronic equipment, various automobile parts, and various daily necessities, can be provided at low cost. . In addition, the foam injection molding method of the present invention includes not only ordinary thermoplastic resins but also flame retardants having low thermal stability, resin compositions which are difficult to mold at high resin temperatures, and low flowability. The conventional method can be advantageously applied to resins for which injection molding is difficult.

Claims

Range of request

1. A foam injection molding method for a thermoplastic resin, the method comprising '

The mold cavity has an inner wall surface and communicates with a resin inlet.

The inner wall surface of the mold cavity has a molten resin discharging means,

As a result, a foamable molten resin mass is formed in the mold cavity,

(3) The foamability is increased by applying pressure to the foamable molten resin mass in the mold cavity and pressing the surface of the foamable molten resin mass against the inner wall surface of the mold cavity. The surface portion of the molten resin mass is solidified to form a skin layer of the foamable molten resin mass, and

(4) A part of the foamable molten resin mass is Due to the foaming pressure of the body, the molten resin is discharged to the outside of the mold cavity through the molten resin discharge means to reduce the pressure on the foamable molten resin mass, thereby reducing the pressure in the mold cavity. Foaming the molten resin mass to form a substantially non-foamed foamed resin mass having the skin layer;

A foam injection molding method characterized by the above.

2. Pressurizing the foamable molten resin mass in step (3) by injecting additional foamable molten resin into the mold cavity to apply a predetermined resin holding pressure to the foamable molten resin mass. The method according to claim 1, wherein the method is performed.

The method according to claim 1 or 2, wherein the pressure is such that the foamable molten resin injected in (2) does not cause foaming in its flow front.

4. The method according to claim 3, wherein the pressurized gas introduced into the mold cavity before step (2) and after step (1) is carbon dioxide gas.

5. The molten resin discharging means of the mold cavity is an on-off valve, The mold has a molten resin discharge cavity that communicates with the mold cavity through the on-off valve, and the volume of the molten resin discharge cavity is increased by the on-off valve in step (4). The method according to any one of claims 1 to 4, wherein the volume of the foamable molten resin mass discharged to the outside of the mold cavity is larger than the volume of the part.

6. The method according to claim 5, wherein the molten resin discharging cavity has an air opening communicating with the outside of the mold.

7. The foamable molten resin comprises the molten resin and at least one gaseous foaming agent dissolved therein, and the at least one gaseous foaming agent comprises carbon dioxide gas and nitrogen gas. The method according to any one of claims 1 to 6, wherein the method is selected from the group consisting of:

8. The method according to claim 7, wherein the content of the foaming agent in the foamable molten resin is 0.05 to 10% by weight.

9. A foam injection molding method for a thermoplastic resin,

The mold cavity has an inner wall surface, and a resin inlet and a location. It leads to the gas inlet if desired,

The inner wall surface of the mold cavity has a molten resin discharging means,

As a result, a foamable molten resin mass is formed in the mold cavity,

(4) At least a part of the foamable molten resin mass and at least a part of the pressurized gas in the gas-filled hollow portion are subjected to the foaming pressure of the foamable molten resin mass itself and the gas pressure in the gas-filled hollow portion. Due to the pressure of the pressurized gas, the outside of the mold cavity is discharged through the molten resin discharging means. Discharging to reduce the pressure on the foamable molten resin mass, thereby foaming the foamable molten resin mass in the mold cavity to form a foam having the substantially non-foamed skin layer. Forming a resin mass,

A foam injection molding method characterized by the above.

10. The method according to claim 9, wherein the pressurized gas used in step (3) is carbon dioxide gas.

11. Before the step (2) and after the step (1), pressurized gas is introduced into the mold cavity to increase the pressure of the mold cavity.

The method according to claim 9 or 10, wherein the pressure is such that the foamable molten resin injected in (2) does not cause foaming in the flow front.

12. The method according to claim 11, wherein the pressurized gas introduced into the mold cavity before step (2) and after step (1) is carbon dioxide gas.

13. The molten resin discharging means of the mold cavity is an open / close valve, and the mold has a molten resin discharge cavity that communicates with the mold cavity through the open / close valve. In step (4), the volume of the molten resin discharging cavity is passed through the on-off valve to the mold. The method according to any one of claims 9 to 12, wherein the volume of the foamable molten resin mass discharged to the outside of the cavity is larger than the volume of the portion.

14. The method according to claim 13, wherein the molten resin discharging cavity has a ventilation hole communicating with the outside of the mold.

15. The foamable molten resin comprises the molten resin and at least one gaseous foaming agent dissolved therein, and the at least one gaseous foaming agent comprises carbon dioxide gas and nitrogen. The method according to any one of claims 9 to 14, wherein the method is selected from the group consisting of gas.

16. The method according to claim 15, wherein the content of the foaming agent in the foamable molten resin is 0.05 to 10% by weight.